Central Bureau for Astronomical Telegrams
IAUC 6565: GX 17+2; 46P
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Circular No. 6565
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
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GX 17+2
M. van der Klis, J. Homan, and R. Wijnands, Astronomical
Institute 'Anton Pannekoek', University of Amsterdam (UA); E.
Kuulkers, Oxford University; F. K. Lamb and D. Psaltis, University
of Illinois at Urbana/Champaign; S. Dieters, University of Alabama
at Huntsville (UAH); J. van Paradijs, UAH and UA; W. H. G. Lewin,
Massachusetts Institute of Technology; and B. Vaughan, California
Institute of Technology, report: "RXTE observations of the Z-source
and low-mass-x-ray-binary GX 17+2 that we obtained during Feb. 6-9
show quasiperiodic oscillations (QPOs) at the kHz level. We find
two peaks in the power spectra of the x-ray countrate variations.
The frequency of the lower-frequency peak decreases from about 880
to 682 +/- 5 Hz when the countrate increases from 1600 to 1920
counts/s. This is consistent with a positive correlation between
frequency and mass-accretion rate, as the source is on the normal
branch in the x-ray color-color diagram during our observations,
where countrate and accretion rate are thought to be anticorrelated.
The higher-frequency peak is detected only at high countrate, at a
frequency of 988 +/- 3 Hz. The peak separation is then 306 +/- 5
Hz. Peak widths range from 30 to 200 Hz, and QPO amplitudes are
between 3 and 5 percent (rms), with no significant dependence on
countrate. We also observe simultaneous horizontal-branch
oscillations of about 60 Hz, but no 6-Hz QPOs, consistent with the
source being in the upper-normal branch. The kHz QPOs were
detected in the band 8-60 keV and are very difficult to see in the
more usual 2-60-keV band. X-ray observers are advised to use high
time-resolution modes, which allow isolating the high-energy
photons, in ongoing observational programs of bright low-mass x-ray
binaries in order to be able to detect the phenomenon."
COMET 46P/WIRTANEN
J.-L. Bertaux, on behalf of the SWAN team at Service
d'Aeronomie, Paris, and the Finnish Meteorological Institute,
Helsinki, writes: "The Lyman-alpha emission of the hydrogen
envelope of comet 46P was observed for the first time on Feb. 10
(at r = 1.15 AU) with the SWAN experiment onboard the SOHO
spacecraft at the L1 Lagrange point (the spacecraft being 1.61 AU
from the comet). From the peak intensity of 44 rayleighs in SWAN's
1 deg field-of-view, the water-production rate is estimated at 7 x
10E27 molecules/s, using a comparison with a simple Haser model."
(C) Copyright 1997 CBAT
1997 February 22 (6565) Daniel W. E. Green
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